Heat gas grill on medium-high or charcoal grill until coals are ash white.,Layer 2 slices cheese onto 2 slices bread; top with remaining bread slices.,Spread outside of bread slices with butter.,Place onto grill.,Cook, turning once, 5-8 minutes or until golden brown.,Cool slightly.,Cut into 1-inch cubes.,Place halved romaine lettuce heads directly onto grill.,Cook 2-3 minutes or until grill marks appear.,______,Remove lettuce heads to serving plates.,Top each with croutons, bacon, onion slices and dressing.,Serve with additional dressing, if desired.